Cw Laser Annealing Research Articles

Aligned, Coexisting Liquid and Solid Regions in Pulsed and CW Laser Annealing of Si

ABSTRACTAligned, coexisting liquid and solid regions are observed in cw laser annealing of polycrystalline Si films on quartz substrates. These stripe patterns are the precursors of surface topography that exists after cooling. It is proposed that a similar situation exists in the pulse annealing process. A calculation of the temperature evolution which assumes stripe symmetry and kinetic restraints of the crystallization process has been carried out. These calculations indicate a lattice temperature of between 1100 and 1300 K, 10 nsec after the sample has fully solidified.

Pulsed and cw laser annealing of polysilicon films

Pulsed and cw laser annealing of polysilicon films

CW laser annealing of A15 superconductors

The change in superconducting transition temperature (T c ) induced by cw laser annealing has been studied for various A15 compounds. Ordering of disordered Nb 3 Sn starts to occur after a single laser scan, making possible an estimation of the activation energy for ordering at high temperatures (1000–2000°C) for times < 0.1 sec. In contrast, laser annealing of well-ordered high T c Nb 3 Sn and V 3 Si is found to alter both the resistivity and the T c . Metastable high T c Nb 3 Ge shows a marked non-monotonic dependence upon annealing temperature which is believed to arise from the formation of a low T c phase at intermediate annealing temperatures.

CW laser annealing of boron and arsenic-implanted silicon; electrical properties, crystalline structure and limitations: A. Gat, T. J. Magee, J. Peng, V. R. Deline and C. A. Evans, Jr. Solid-State Technol. p. 59 (November 1979)

CW laser annealing of boron and arsenic-implanted silicon; electrical properties, crystalline structure and limitations: A. Gat, T. J. Magee, J. Peng, V. R. Deline and C. A. Evans, Jr. Solid-State Technol. p. 59 (November 1979)

Luminescence investigations of laser-annealed Si

Low-temperature photoluminescence has been used as a minority-carrier probe to investigate the perfection of laser-annealed Si. For cw laser annealing of ion implantation damage, the range of laser power over which good quality annealed material can be achieved, as determined by the relative luminescence efficiency, is limited. At high laser power, when laser-induced damage has been observed by other techniques, a slight broadening and shifting of the bound-exciton luminescence lines was seen. From these data, the residual strain surrounding the implanted ions was found to be small for the low doses employed in this study, with lattice displacements of less than ∼0.01%. These results imply that laser annealing can give rise to high-quality material suitable for device application if sufficient care is exercised.

Cw laser annealing of Nb3Al and Nb3Si

cw laser annealing has been applied to synthesize the metastable A15 superconductors, Nb3Al and Nb3Si. Qualitative agreement with the equilibrium phase diagrams have been obtained for the Nb-Al system. Laser annealing permits the high-temperature A15 phase to be fast quenched to room temperature without decomposition. Subsequent use of multiple low-temperature laser scans raises the superconducting transition temperature, probably by improving the atomic order. For the Nb-Si system, a single-phase nonstoichiometric A15 structure is formed from the amorphous phase upon laser annealing.

Seeded and limited seeding regrowth of Si over SiO2 by cw laser annealing

Single-crystal Si sheets (0.2 μm in thickness) of (100) orientation and of maximum dimensions, 100×10 000 μm, have been recrystallized by cw laser annealing of poly crystalline Si films deposited over parallel 3-μm-wide SiO2 bars adjacent to 3-μm Si (100) substrate openings. The recrystallized films are free of cracks, mosaic structure, stacking faults, or excessive mass flow at the oxide edges. In a correlated series of experiments we have shown that the Si can be recrystallized over the SiO2 with only limited or relaxed requirements for vertical seeding from the substrate window.

Slip dislocation formation during cw laser annealing of silicon

High-voltage electron microscopy (HVEM) has been used for the investigation of the defect structure in cw laser-annealed silicon. We report for the first time a (HVEM) analysis of the formation processes involved in the nucleation and glide of slip dislocations during epitaxial regrowth by cw laser annealing of ion-implantation damaged silicon layers. Based on the combined optical and HVEM observations a model of the dislocation generation and glide processes is presented.

Improved performance of 4K SRAM by means of CW laser annealing

A 4K × 1 NMOS static RAM (MM2147) has been successfully fabricated by means of CW laser annealing. The access time was reduced by 10 ns compared with a thermally annealed control with no increase in power dissipation. This report demonstrates the feasibiligy of using CW laser annealing as a potential VLSI process technology.

Defect Formation in CW CO2 Laser Annealed Silicon

ABSTRACTThe EBIC mode of the SEM has been used to investigate the perfection of cw CO2 laser annealed Si. Even in material that contains no slip lines, non-uniform charge collection is found. A combined X-ray and electron microscopy (TEM, SEM) study identified the residual defects responsible for the EBIC contrast as interstitial submicron dislocation loops. Scanning cw laser annealing independent of the wavelength (10.6μm or 0.514μm) always introduces residual defects which act as recombination centers and reduce minority carrier lifetime.

Competition Between Solid Phase Epitaxy and Random Crystallization During cw Laser Annealing of Amorphous Si Films

ABSTRACTThe kinetics of amorphous-to-polycrystalline conversion and solid phase epitaxy (SPE) in UHV-deposited Si films have been determined over a wide temperature range by the use of optical reflectivity measurements made during rapid heating by a cw Ar laser. Crystallization rates measured in UHV following film deposition are reported and compared to rates measured in air in order to elucidate the effects of contaminants on the processes. The effects of boron doping on nucleation and growth kinetics are also reported. The crystallization rates determined in these studies can be used to predict the volume fraction of polycrystalline material formed during laserinduced SPE growth of thick epitaxial layers.

Cw laser annealing of hydrogenated amorphous silicon obtained by rf sputtering

Hydrogenated amorphous silicon obtained by rf sputtering has been annealed using cw lasers (Ar or Kr ion). The annealed films have been microanalyzed for quantitative profiling of hydrogen and argon. TEM analysis was used for structure determination. The release of hydrogen and argon as well as the grain size of the polycrystalline material obtained are related to the deposited laser energy. Comparison with other production methods of such material from the amorphous state is discussed.

Epitaxial Ge/GaAs Heterostructures by Scanned CW Laser Annealing of a-GE Layers on GaAS

ABSTRACTEpitaxial regrowth of Ge/GaAs heterostructures by scanned laser annealing of amorphous Ge films on GaAs substrates has been studied as a function of laser power and scan rate. At least eight regimes representing different film regrowth characteristics were observed. Of these, two were of primary interest. At low powers (between~1.6 and 3.2 W for a beam diameter of~40 μm) and scan rates between 1 and 400 cm/sec, polycrystalline Ge with a (100) preferred orientation was formed by an “explosive” crystallization mechanism. At higher powers, and over a scan rate range of 25 to 400 cm/sec, single crystal metastable (GaAs)1−x Gexalloys were obtained by liquid phase regrowth. Typical film resistivities, ρ, were as follows: as-deposited ρ=180Ωcm; polycrystalline films, ρ=3 × 10−2 Ωcm; single crystal films,ρ=9×10−4Ωcm.

Modelling of CW Laser Annealing of Multilayer Structures

ABSTRACTA thermal model is developed for cw laser annealing of multilayer structures. Each layer has arbitrary thickness, thermal conductivity and optical properties. Steady state conditions with no phase transition are assumed. A procedure is presented for obtaining the temperature distribution in any system and explicit integral expressions are developed for the two and three layer cases. Results are calculated for the Si/glass and Si/SiO2 /Si systems.

Fast Scan Laser Annealing

ABSTRACTLaser-annealing phenomena have typically been divided into two distinct realms. Pulsed lasers involved very short anneal times and small deposited energy densities. Slowly scanned cw lasers involved intermediate times (ms range) and larger energy densities. Repetitively scanned electron beams have extended the range of anneal time and energy density toward conventional thermal processing. This paper examines the regime between pulsed laser annealing and conventional cw laser annealing. By greatly increasing the scan speed of the laser, annealing times and deposited energy densities are reduced and approach those of pulsed laser annealing. Applications are discussed in the areas of silicon-on-insulator recrystallization, low resistivity poly, vertical integration, local lateral seeding, explosive crystallization, and line-source simulation.

Study of the Crystalline to Amorphous Silicon Boundary Following Laser Induced Solid Phase Epitaxy.

ABSTRACTEBIC and voltage contrast SEM microscopy, combined with optical microscopy. chemical etching and Talystep profiling have been used to investigate cw laser annealing of a-Si in the slip-free SPE regime. Special attention is devoted to the edges and extremities of the line scans, i.e. to the c-to a-Si boundary. At very low power, evidence is given for an initial reordering and thus electrical activation stage of the a-Si. For the higher power range regrowth occurs through two different processes. The EBIC yield is interpreted in terms of a balance between annealing of the ion implantation damage and defect generation in the si substrate during the laser annealing. These results are extended to the case of a scanned electron beam annealing.

Direct observation of laser-induced solid-phase epitaxial crystallization by time-resolved optical reflectivity

Direct measurement of solid phase epitaxial crystallization during cw laser annealing of ion-implanted silicon is reported. The measurement technique utilizes optical interference effects between reflected light from the sample surface and from the epitaxial growth plane to time-resolve the growth process with high spatial resolution. Laser-induced solid phase epitaxial growth was monitored for two values of incident laser power; corresponding epitaxial growth rates and calculated surface temperatures are given.

Electron-beam-induced current investigations of cw laser-annealed silicon

The electron-beam-induced current in As+-implanted Si is investigated after cw laser annealing. These experiments show that the laser power ’’window’’ for successful laser annealing is quite small; low charge collection efficiency usually results. To date, the best annealing results were obtained for a highly overlapping laser scan (100-μm beam with 6-μm scan steps), at a laser power approximately 70 –75% of the power required for melting. At higher laser power, evidence for laser-induced damage has been observed. This evidence suggests that the damage extends several microns below the implanted layer.

A general analytic technique for nonlinear dynamic transport processes during laser annealing

We present an approximate analytic technique capable of describing the dynamics of nonlinear heat and mass diffusion. The technique is based on using adiabatic approximation in the Green’s-function formulation and is illustrated for the case of heat transport during pulsed and cw laser annealing of Si. In particular, the heating efficiency is discussed explicitly as a function of pulse intensity for a fixed pulse energy.

CW laser annealing of boron and arsenic-implanted silicon; electrical properties, crystalline structure and limitations: A. Gat, T. J. Magee, J. Peng, V. R. Deline and C. A. Evans, Jr.Solid-St. Technol. p. 59 (November 1979)

CW laser annealing of boron and arsenic-implanted silicon; electrical properties, crystalline structure and limitations: A. Gat, T. J. Magee, J. Peng, V. R. Deline and C. A. Evans, Jr.Solid-St. Technol. p. 59 (November 1979)